docs: def subscribe(obj, event, callback, event_state=None):
      """Subscribe an event from an class.
  
      Subclasses of the class/object will also fire events for this class,
      unless a more specific event exists.
      """
      if inspect.isclass(obj):
          cls = obj.__name__
      else:
          cls = obj.__class__.__name__
  
      if event_state is None:
          event_state = states.ANY
  
      event_key = '.'.join([cls, event, event_state])
      if event_key not in EVENT_HANDLERS:
          EVENT_HANDLERS[event_key] = []
  
      EVENT_HANDLERS[event_key].append(callback)
      return